This invention relates to a wake-up alarm, and more specifically relates to a wake-up alarm which is inhibited while the subject is in a deep-sleep phase.
When a human sleeps, he passes through different sleep phases which include a deep-sleep, rapid eye movement (REM) sleep and shallow-sleep phases. The phases can be identified by the state of one or more of several physical or physiological conditions including brain wave activity, REM, pulse rate, muscle tension, body temperature, hearing acuity, blood pressure, respiratory rate, body position changes, and others. As a specific example, when a human sleeps, he passes through a deep-sleep phase characterized by delta brain-wave frequencies which are less than about 4 hertz, and more shallow sleep phases characterized by the relatively high frequencies known as beta brain-wave frequencies, which are greater than about 13 hertz. REM sleep resembles a shallow-sleep phase when only brain waves are considered. However, the presence of REM or the absence of muscle tension or other indicators can be used to detect REM phase sleep.
The deep-sleep and REM phases are relatively short and it is believed that these are the most efficient sleep phases. It is desirable that a subject is awakened from sleep during the light-sleep phase. This recognition, however, has never been implemented in connection with the waking up of a sleeping subject.
Many prior patents have been obtained for systems wherein an alarm is given or some other signal is produced in response to the monitoring of the brain waves of a subject which would indicate that he is falling asleep or that he is experiencing a medical catastrophy. These systems have obvious use in connection with the waking of a dozing driver or the monitoring of a patient who might, for example, be in an intensive care situation. These systems will normally produce an output signal in response to brain-wave frequencies such as beta frequencies which appear in a subject who supposedly is in an alert state and passes into a state of light sleep. There is no attempt, however, in these prior art arrangements of inhibiting the production of an output alarm while the subject is in a deep-sleep or REM phase.
Typical of prior art references which monitor a normally alert subject for change in brain-wave frequencies indicating either a state of drowziness or a medical catastrophy are U.S. Pat. Nos. 3,811,116; 3,863,243; 3,866,204; 3,875,929; 3,877,466; 3,890,957; 3,896,790; 3,924,606; 4,013,068; 4,037,586.
A typical circuit which can be used to indicate the presence of alpha activity is disclosed in the journal "Psychophysiology", Volume 8, Number 1 (1971), pages 107 to 112, entitled "A Hybrid Circuit to Indicate the Presence of Alpha Activity".
Another reference showing circuitry well suited for such applications is NTIS document number AD/A-002 665 "Spindle and Rapid Eye Movement Detectors for Use with Sleep Analyzers", by Joseph C. Christian. This document also references many other documents that give details about alternative circuits that may be used to decode sleep stage information from brain waves. Another method that can be used is described by Anand Kumar, "A Real-Time System for Pattern Recognition of Sleep Stages by Fuzzy System Analysis", contained in Pattern Recognition, Vol. 9 (1977), pages 43 to 46.